Notch filters are placed in the track following and seeking control loops in conventional servo control systems to help stabilize the actuator mechanics. These notch filters are typically mathematically implemented in algorithms defined in the drive control firmware. The particular placement parameters utilized in these notch filter algorithms may be stored in the boot record on the disc or permanently stored in the firmware. To compensate for drive-to-drive variations, notch filter placement is customized for each drive and each head within a drive. Since each head in every drive requires its own set of specific notch filters, notch filter placement is accomplished as part of a manufacturing test process that customizes, tunes, and validates every drive.
Servo Notch Optimization (SNO) is the portion of the post assembly manufacturing test process that places the notch filters. Due to memory limitations, the factory test systems that perform this portion cannot acquire the necessary number of data points to optimize the entire frequency range of interest in disc drive operation. Thus, the current SNO requires that the frequency spectrum of each head be divided into a series of smaller ranges. The SNO process then places only one notch per sub-range. Ideally, each sub-range will only contain one resonance peak that needs to be notched since the current SNO process only allows one notch per range.
The current conventional SNO process has several shortcomings. First, it requires prior identification of the resonances that will require notch filters. Second, it requires that the center frequency of the previously identified resonances be consistent from drive to drive. Third, as previously mentioned, the SNO process only allows for one notch per range. The current conventional SNO process is inadequate, due to drive-to-drive frequency variations and the one notch per sub-range limitation, in the case of double peaked resonances that require two notches for appropriate coverage. Accordingly there is a need for a more versatile method for notch filter placement in a disc drive control scheme. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.